Describe the characteristics and types of primary rocks.

Primary rocks are formed at the first instance in the geological time scale and are result of solidification of magma and lava like granite, gabbro, pegmatite, basalt.

Characteristics:

• Hard and resistant to erosion.
• Sudden cooling results in small and smooth grains and slow cooling results in large-sized grains.
• Primarily eroded by mechanical weathering.
• Water seepage is low and hence does not have high groundwater levels
• Lack fossil deposits but are rich in ferrous deposits.

Types:

Depending upon their location there are following types of primary rocks:

Intrusive rocks:

• Formed due to cooling and solidification of magma within the Earth crust.
• Associated with features like dykes, batholiths, laccoliths, phacoliths etc.
• They generally have large crystals.

Extrusive rocks:

• Formed due to cooling and solidification of lava on the surface of the Earth.
• They have small-sized crystals.

These primary rocks can help us to study the earth’s interior and have high economic importance. UNESCO’s global framework for geo-heritage can go a long way in guiding countries to conserve their landforms.